So my 1986 4.2 is exhibiting odd behavior again two weeks after changing the starter. I was having slow cranks, and the Volts gauge usually marked the 13 on the gauge, but it left me stranded and I managed to get it running by tapping the starter. I figured the problem was the starter so I replaced it. It was fine and it was sounding like it should when starting. Nice and healthy. I got the AC working again this past weekend and suddenly the car is hesitating to crank again. Once the car gets running again the Volts gauge reads below 13, which is not where it used to be. So I went to a shop and bought a new Interstate battery. On the first go, it was no different from my original battery. So I reinstalled my old battery. Where do I start before throwing a new alternator at it?

 

Battery cable ends clean and tight, including the "-" cable where it attaches to the body.
Main engine ground clean and tight. Under the car, right side, about where the engine and transmission come together.
Firewall "+" junction posts clean and tight.

If no improvement in voltage reading check the resistance/condition of the alternator output wire, that fat one from the alternator to the LH side junction post on the firewall. Sometimes these become packed with corrosion...hidden under the insulation.

Of course the alternator itself could be marginal and ready to give up the ghost. But I'd check all the above first.

Cheers
DD

 

After carrying out Doug's suggestions and with no improvement I think you may have an alternator problem.
I had similar problems in my S3 a few years ago. The battery always seemed a bit flat with poor cranking and the voltmeter needle was sitting low somewhere around 12 volts when running which I confirmed with a multimeter.
It turned out that one diode in the alternator had failed and when the car was parked there was a drain on the battery through the failed diode.
In addition the battery was not getting a decent charge as typical voltages for battery charging on a 12 volt system are around 13.8 to 14.2 volts.
Cheers

 

Not running, my volt meter states 12.9V at the battery leads. Running it reads 13.7 Not what the car gauge reads.

 

No expert, but the slow crank with a new battery and the measured voltages would not indicate an issue with the alternator. I think Doug is on track with the power getting to the Starter (poor conections etc).

 

I agree. I cleaned the battery terminals and clamps, I cleaned the ground at the battery and fender. Replaced the transmission to body strap with an insulated cable and cleaned the contact points with a small wire wheel. I noticed a bit of improvement. But I made a bigger discovery just a few moments ago. The positive cable looks weak and frayed at the clamp. Im sure my problem is there. Will have to replace the entire cable but Im going to try replacing the clamp first. Heres what I saw once the brittle rubber cracked right off. The brittle wires have cracked near the crimp and the clamp is probably hanging by a few threads.

 

I think you are on the right path, with the wiring and poor connections.

And sorry to say this, but I also think this is a textbook example of throwing parts at a car (new starter, new battery) and hoping that will fix things...without looking for a cause.

 

No Wilfred. The starter did quit on me, Smacking it got me going again a few weeks ago, as for the battery, its 5 years old so its time for it to go. Im doing my homework before replacing anything else. So its not a textbook. example of throwing parts at it. Its why I started this post. Once the terminal gets replaced, Ill throw in my new battery. No harm done.

 

13.7 volts from the alternator is quite OK. So you don't have to go down that path
There are heaps of aftermarket battery clamps available so you don't have to replace the cable - just the clamp end..
5 years is a pretty good life for a battery but it would be getting close to the end of life. I would be seriously looking at the "new" battery for future trouble free motoring.
Cheers

 

Thanks for the input fellas! I managed to get a set of custom cables for Etype and XJ6, at my local indy shop. Its made a considerable difference, once I installed them, still have to go through the Earth points and clean them all up for peace of mind

 

God I hate those standard battery hold downs that surround the top of the battery with just millimeters between the clamp and a fully earthed hold down. Changing that and putting some boots over the two big battery bulkhead connectors (mine had rotted off) were one of the first jobs I did on my car when I got it. A bit paranoid about electrics in old cars I am.